1. Field of the Invention
The present invention relates to a low dielectric constant insulating film and a method of forming the same.
2. Description of the Prior Art
In recent years, an insulating film having a low dielectric constant (hereinafter, referred to as a low dielectric constant insulating film) is used in a semiconductor integrated circuit in order to suppress the delay of signals communicating in wirings and to improve the processing speed of the entire circuit.
Although a semiconductor roadmap requires an interlayer insulating film having a relative dielectric constant of 2.5 or less in and after a generation when a design rule becomes. 65 nm, it has turned out after studying various insulating materials that it is difficult to realize the relative dielectric constant of 2.5 or less with raw (non-porous) material. For this reason, there has been used a way such as reducing the effective dielectric constant of the entire insulating film by reducing a film density while employing an insulating material having the relative dielectric constant of 2.5 or more. It is a method such that pores of nanometers to sub-nanometers are introduced in a formed insulating film to make it porous and thus reduce a film density.
For example, Patent Document 1 describes an example to make it porous by introducing dopant into the formed film and then removing it from the film by oxidation or the like.
[Patent Document 1]
Japanese Patent Laid-open 2000-273176 publication
However, when the pores are introduced in the insulating film to make it porous, there occurs a problem such that mechanical strength of the entire film is reduced significantly and thus the film cannot withstand a polishing process (CMP: chemical mechanical polishing) performed for planarization in process after deposition. To solve the problem, a pore size is made smaller or the porosity is reduced. With this, although the mechanical strength of the film is improved, a low relative dielectric constant so as to be required is not obtained.